I always would like to Ning add text box in Forum to we could add some text, informations or other stuff for my members. Hehe but we can only wish.
So I create today code thanks we could add content to Forum - not description of category ;)

Effect you may see on my site HERE, under the search bar.

So we start :D
1. Go to dashboard.
2. Go to Analitics.
3. Add code:

<script type="text/javascript">
x$("#.categories, .byCategory").before('<div>your text, your text</div>');
</script>

Sorry form my english I hope you understand everything :)